Field of the Invention
The present invention relates to a method for producing a toner particle used in an electrophotographic process, electrostatic recording method or magnetic recording method and the like.
Description of the Related Art
Numerous inventions have been provided that relate to toners produced by a wet toner particle production method, such as a suspension polymerization method or emulsion polymerization method using a polymerizable monomer or the like, or a dissolution suspension method in which a binder resin and the like is granulated in a solvent.
Toner produced in an aqueous medium or organic solvent as in the suspension polymerization method or emulsion polymerization method has an extremely sharp particle size distribution. Consequently, in addition to being able to realize high developing performance and high transferability, high yield can also be achieved, thereby making the toner superior from the viewpoint of productivity.
Toner produced using a wet method is obtained by forming a toner particle in an aqueous medium or organic solvent to obtain a toner particle-dispersed solution, followed by separating the toner particle from the toner particle-dispersed solution using a separation means, typically represented by solid-liquid separation device in the manner of a filtration device, and subsequently adding an external additive as necessary.
In recent years, photocopiers and printers using an electrophotographic method have come to be required to offer faster speed, higher image quality and reduced size, and high-definition images are required to be provided despite increasing device process speeds. Since the load on the toner increases as process speed becomes faster, there is increased the occurrence of problems relating to developing performance such as fogging of non-image areas due to toner deterioration particularly in environments at low temperature and low humidity. In addition, from the viewpoint of high-definition images, a developing system in which the toner carrying member and electrostatic latent image bearing member are arranged in contact (to be subsequently referred to as a “contact development system”) is preferable. However, contact development systems place a greater load on the toner since the toner is subjected to pressure between the toner carrying member and the electrostatic latent image bearing member. It is even more important to enhance toner toughness under such circumstances.
However, from the viewpoint of productivity, it is also necessary to shorten the amount of time consumed by each process during the course of toner production. Toner produced using a wet method is produced under various temperature conditions in a series of steps involving a material dispersion step, colored particle formation step, polymerization step, filtration step and drying step. Among these, productivity can be improved considerably by shortening the amount of time consumed during the process of returning the toner from a high temperature as in the polymerization step or drying step in particular to a normal temperature in a subsequent step.
However, sudden changes in temperature cause the occurrence of differences in the degree to which materials adhere to the binder resin in the toner particle due to, for example, differences in the coefficient of thermal expansion between materials used therein. This tendency is particularly prominent in the case of toner containing magnetic powder as colorant since the coefficient of thermal expansion of the magnetic powder differs greatly from that of other materials. Cracking, chipping and other problems tend to occur resulting in inferior durability in the case toner is subjected to stress over a long period of time as a result of a decrease in adhesiveness.
Numerous inventions have been provided that improve toner performance by removing impurities using a separation device simultaneous to separate colored particles from an aqueous medium during production using a wet method. For example, Japanese Patent Application Laid-open No. 2004-258601 proposes a method for removing impurities present in toner slurry by using a filter having two or more types of meshes during solid-liquid separation. In addition, Japanese Patent Application Laid-open No. H8-137131 similarly proposes a method for removing impurities in toner slurry by using a screw decanter type of continuous centrifugal settler.